Injured Pato to miss most of Milan run-in
The Brazilian limped out of Saturday's 3-0 win over Sampdoria and Milan said in a statement that scans had showed a muscle pull.
The absence of Pato and Zlatan Ibrahimovic, who is suspended for two more league games, means Robinho and Antonio Cassano are the only forwards available to the club.
Ibrahimovic, though, can play in Wednesday's Italian Cup semi-final first leg against Palermo.
Napoli's 2-1 home defeat by Udinese on Sunday gave Milan a six-point lead with five games left and even their cautious coach Massimiliano Allegri has said a first scudetto since 2004 is now in sight.
Third-placed Inter Milan lost 2-0 at strugglers Parma on Saturday to all but wave goodbye to their title after five straight scudettos but president Massimo Moratti has backed new coach Leonardo.
Media reports have said last season's Inter treble winner Jose Mourinho might return to the club from Real Madrid next season.
"I've read what the newspapers say about Mourinho but there's nothing in it," Moratti told reporters while acknowledging his side, also dumped out in the Champions League quarter-finals as holders, were in "crisis".